1. Field of the Invention
This invention relates to a disk apparatus for recording data on or reproducing data from an optical disk, for example.
2. Description of the Related Art
As is well known in the art, various disk drive apparatuses are developed. As one of such disk apparatuses, an optical disk apparatus for recording data on an optical disk and reproducing the data from the optical disk is provided, for example. An example of such optical disk apparatus is that disclosed in U.S. Pat. No. 4,641,294. The optical disk apparatus records data on the optical disk, and reads out the data recorded on the optical disk by a laser light generated from a semiconductor laser in an optical head.
The access control for such an optical disk apparatus is disclosed, for example, in U.S. Pat. No. 4,375,091. To perform the access operation, a linear motor is first driven, thus moving an optical head, thus effecting a rough access. Then, a track on the optical disk is read by means of the optical head thus roughly accessed, and a difference between the detected track and a destination track is determined. At this time, if the difference between the accessed track and the destination track is small, an objective lens is moved by means of an objective lens driving mechanism to effect fine access. However, if the difference is large, the linear motor is driven again to move the optical disk so as to effect rough access. Thus, the optical disk apparatus controls access to the destination track.
The optical disk used in the optical disk apparatus has recording tracks (recording grooves) which are provided in the form of concentric circles, or recording tracks which are formed as a recording groove in a spiral form. In the optical disk having the recording tracks arranged in the form of concentric circles, each recording track is used as the same track or one track. In contrast, in the optical disk having the recording tracks arranged in the spiral form, there is no physical boundary between the tracks, and therefore each track segment corresponding to one rotation of the optical disk is used as an address for locating data, that is, the track segment of one rotation starting from sector "0" is used as the same track or one track for efficient access. Therefore, the access operation in this type of optical disk is effected by simply moving the objective lens by a difference between the detected track number and the destination track number.
However, in the optical disk having the recording tracks of the spiral form, useless access operation may be effected and the access time may be unnecessarily made long. That is, the optical disk has the following problems.
(1) In a case where a currently accessed track lies outside and adjacent to the destination track and the objective lens is moved by one track inwardly, the optical disk will rotate during the time of the one-track movement. In this case, if the objective lens has passed sector "0", it will be set on the same track as that on which it was set before the movement, and therefore it is necessary to move the objective lens again.
(2) In contrast, in a case where a currently accessed track lies inside and adjacent to the destination track and the objective lens is moved by one track outwardly, the optical disk will rotate during the time of the one-track movement. In this case, if the objective lens passes sector "0", it will apparently move outwardly by two tracks, and therefore it becomes necessary to move it inwardly by one track.
In the two cases described above, when sector "0" is passed, it is required to effect an extra access operation, and thus the access time is made longer.